A color image forming apparatus that superimposes plural images to obtain a color image performs alignment of the plural images, prevents blurs and bleeding of the images, and maintains satisfactory image quality. An image forming apparatus that obtains a color image using a traveling belt images an adjustment pattern for alignment adjustment on the belt and aligns plural images using a detection result obtained by detecting the adjustment pattern. The thickness of the belt varies depending on regions of the belt. Since the image forming apparatus aligns the images taking into account the thickness that varies depending on the regions of the belt, during alignment adjustment, the image forming apparatus images plural adjustment patterns over the entire circumference of the belt. The image forming apparatus averages detection results obtained by detecting the plural adjustment patterns imaged over the entire circumference of the belt. The image forming apparatus aligns the plural images using an average obtained by averaging the detection results to thereby improve accuracy of the alignment.
However, if the image forming apparatus images the plural adjustment patterns over the entire circumference of the belt and obtains an average of the plural adjustment patterns every time the image forming apparatus performs the image alignment adjustment, time required for the image alignment adjustment is long. Therefore, it is likely that the image forming apparatus keeps a user waiting during the image alignment adjustment.